Abstract: OBJECTIVE To investigate the effect of anterior caudal block with morphine for postoperative analgesia after hemorrhoidectomy and its possible adverse effects. METHODS Sixty patients scheduled to perform hemorrhoidectomy were randomized into three groups with various dosages of morphine in combination with local anesthetics lidocaine(1%) and ropivacaine(0.375%) using single caudal anesthesia. Group Ⅰ: 1.5 mg of morphine; Group Ⅱ: 2 mg of morphine; Group Ⅲ: no morphine. Visual Analogue Scale(VAS) was evaluated to assess pain at 4, 8, 16, and 24 hours after surgery. Possible adverse effects such as nausea, vomit, uroschesis, respiratory depress, etc., were also examined. RESULTS VAS scores were significantly lower in group Ⅰ and Ⅱ as compared with group Ⅲ(P<0.05). Patients in group Ⅱ had the lowest VAS among three groups. Patients in group Ⅰ and Ⅱ showed less adverse effects than those in group Ⅲ, but there was no significant difference P>0.05. CONCLUSION Anterior caudal injection of 2 mg of morphine in combination of local anesthetics has significant postoperative analgesia of hemorrhoidectomy with little adverse effects.